Although Attention Deficit Hyperactivity Disorder (ADHD) is considered the most common child psychiatric disorder, little is known about the functional neurological deficits associated with this disorder. ADHD is now considered a chronic disorder in many affected individuals, with symptoms of overactivity, inattention, and impulsivity spanning from childhood through adulthood. As children these individuals are at-risk for academic failure and conduct problems. Adults who have retained the symptoms are more likely to experience occupational difficulties, abuse drugs, develop an antisocial personality disorder, and function less successfully in society. Functional neuroimaging techniques such as positron emission tomography (PET), that assess interactions between behavior and regional brain physiology may lead to the development of a better understanding of ADHD and more effective treatments. The objective of this Mentored Clinical Scientist Development Award is to develop the nominee's skills in applying functional neuroimaging techniques to better understand deficits in ADHD. The major goals of this award are to: 1) Develop into an independent researcher; 2) Study brain-environment interactions in ADHD; 3) Acquire expertise in functional neuroimaging techniques (i.e., PET) as it can be applied to ADHD; 4) Develop an independent laboratory studying brain-environment processes in ADHD. Skills acquired in the training program will be applied to pilot studies to assess the effect of task parameters and methylphenidate on regional cerebral blood flow (rCBF) in PET. Specific aims of the pilot studies are: 1) To assess the effect of practice on rCBF and task performance in ADHD and Control adults; 2) To examine how chronic methylphenidate administration in ADHD adults modulates the effects of practice on task performance and rCBF; 3) Establish further areas of study for the postaward phase for the candidate.